an unofficial title held by a horse that wins the Kentucky Derby, the Preakness, and the Belmont Stakes in a single season.
2.
a usually unofficial title held by someone who wins three major awards or championships in the same year.
British Dictionary definitions for Triple Crown
triple crown
noun
1.
(RC Church) the Pope's tiara
2.
(horse racing) the winning of three important races in one season
3.
(often capitals) (rugby Union) a victory by Scotland, England, Wales, or Ireland in all three games against the others in the annual Six (formerly, Five) Nations Championship Compare grand slam (sense 3)